An automatic impedance matching system, method, and application based on reflection coefficient measurement

Abstract

This invention relates to an automatic impedance matching system, method, and application based on reflection coefficient measurement. The matching system includes a matching network, a reflectometer module, and a control module. The reflectometer module is connected in series between the matching network and the radio frequency (RF) power supply. The reflectometer module measures the reflection coefficient at the output of the RF power supply, and the reflection coefficient includes amplitude and phase information. The control module is connected in series between the reflectometer module and the matching network. The control module adjusts the matching network to change the position of the reflection coefficient on the Smith chart, making it infinitely close to the origin of the Smith chart. The RF power supply displays a reflected power of 0, thus achieving impedance matching. This invention provides a fast, convenient, and accurate matching method for plasma excitation devices. This method avoids blind operation and simplifies the matching process of plasma excitation devices.

Description

Technical Field

[0001] This invention belongs to the field of impedance matching technology for radio frequency circuits, and in particular to an automatic impedance matching system, method and application based on reflection coefficient measurement. Background Technology

[0002] During plasma excitation, radio frequency (RF) power is coupled to the plasma excitation device via an impedance matching circuit, and then transferred to electrons. Electrons undergo inelastic collisions with neutral gas particles, generating plasma. Therefore, proper impedance matching can maximize RF power input and improve the degree of ionization.

[0003] Impedance matching is fundamentally based on a matching network composed of adjustable reactive components. Under different processing conditions, the impedance characteristics of a plasma excitation device often vary. This necessitates adjusting the parameters of the components in the matching network to adapt to different impedance states in the circuit and achieve good matching. Adjusting the matching network parameters typically involves two methods: manual and automatic. In manual matching, the user relies on experience and on-site measurements of parameters such as the reflection coefficient, load, and signal source impedance to manually adjust the component parameters in the matching network. Manual matching is time-consuming, has low matching accuracy, and cannot achieve online dynamic adjustment. Under complex load conditions, it is difficult to achieve stable and efficient matching, ultimately affecting the plasma processing process and quality. In contrast, a well-designed automatic matcher can perform real-time, efficient, and accurate impedance matching, improving the stability of plasma discharge and achieving high-quality processing.

[0004] The reflection coefficient characterizes the impedance matching degree and is of great guiding significance for adjusting the matching network. Real-time measurement of the reflection coefficient and its use as a reference can greatly simplify the process of adjusting the matching network. As a high-power active radio frequency device, plasma excitation devices are difficult to measure using traditional reflection coefficient measurement methods, such as network analyzers or standing wave meters.

[0005] Using the reflection coefficient for impedance matching is a common approach. Most existing related patents apply this approach, but they do not provide a method for measuring the reflection coefficient that includes complete amplitude and phase information. Furthermore, due to the lack of phase information for the reflection coefficient, complex control methods and adjustment algorithms must be used to adjust the matching network, and the applicable impedance networks are relatively limited. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing methods and provide an impedance matching method based on reflection coefficient measurement, which can achieve impedance matching quickly and accurately.

[0007] The technical solution adopted by this invention to solve the technical problem is:

[0008] A first aspect of this invention provides an automatic impedance matching system based on reflection coefficient measurement, comprising a matching network, a reflectometer module, and a control module. The reflectometer module is connected in series between the matching network and the radio frequency (RF) power supply. The reflectometer module measures the reflection coefficient at the output of the RF power supply, and the reflection coefficient includes amplitude and phase information. The control module is connected in series between the reflectometer module and the matching network. The control module adjusts the matching network to change the position of the reflection coefficient on the Smith chart, making it infinitely close to the origin of the Smith chart. The RF power supply displays a reflected power of 0, thus achieving impedance matching.

[0009] Furthermore, the reflectometer module includes: a directional coupler, an attenuator, a phase shifter, a power divider, a vector power meter, and a first microcontroller. The directional coupler couples out two incident signals and one reflected signal from the line. The attenuator is used to compress the amplitude of the first incident signal and the reflected signal. The phase shifter changes the second incident signal into a phase-shifted signal. The power divider splits the phase-shifted signal, the attenuated incident signal, and the reflected signal into two. The vector power meter is connected to the signal output terminal of the power divider and is used to identify the amplitude ratio and phase difference of the two signals. The first microcontroller controls the analog-to-digital converter to read the measurement results of the vector power meter, processes them to obtain the reflection coefficient, displays the results on the display screen, or sends them to the automatic control module for adjusting the matching network.

[0010] Furthermore, the control module includes: a motor, a driver, a second microcontroller, a control panel, and a display screen. The driver is connected to the motor; the second microcontroller is connected to the driver, receives the measurement results from the reflectometer module, and controls the motor via the driver to rotate the variable element parameter adjustment knob in the matching network, thereby adjusting the parameters of the variable element; the control panel is connected to the second microcontroller, and the user controls the start / stop of matching via buttons on the control panel; the display screen displays the Smith chart, the measured reflectance coefficient, and the current working status of the control module.

[0011] The second aspect of this invention provides an automatic impedance matching method for a plasma excitation device based on reflection coefficient measurement. This method utilizes a reflectometer module to measure the reflection coefficient of the circuit at the output of the polarizing power supply in real time and marks the reflection coefficient on a Smith chart. Adjusting the matching network causes changes in the reflection coefficient, and the position of the reflection coefficient on the chart changes accordingly. When a single variable element (such as a variable capacitor or variable inductor) in the matching network is adjusted, the trajectory of the reflection coefficient on the chart approximates a portion of a circle or ellipse. Adjusting different elements in the matching network causes the reflection coefficient to move along different circles or ellipses. The trajectory of the reflection coefficient on the Smith chart is influenced by multiple adjustable elements; that is, the trajectory of the reflection coefficient corresponding to the same variable element differs before and after other variable elements are adjusted. The entire impedance matching process involves adjusting the matching network so that the reflection coefficient, after traversing multiple different approximate circular or elliptical trajectories, finally reaches the origin of the Smith chart, eliminating reflection. This method can be implemented manually or by an automatic control module.

[0012] Furthermore, the reflectometer module separates the reflected signal and the incident signal from the circuit, adjusts the two signals and performs amplitude and phase detection, and further processes the detection results to obtain an accurate reflection coefficient containing complete information.

[0013] Furthermore, the phase-shifted signal, the attenuated incident signal, and the reflected signal are each divided into two equal parts by a power divider, resulting in a first incident signal, a second incident signal, a first reflected signal, a second reflected signal, a first phase-shifted signal, and a second phase-shifted signal. Three vector power meters are used: vector power meter A, vector power meter B, and vector power meter C. Vector power meter A detects the phase difference between the first phase-shifted signal and the first incident signal to obtain the phase shift magnitude provided by the phase shifter. Vector power meter B detects the second incident signal and the first reflected signal to obtain the amplitude ratio and phase difference between the reflected signal and the incident signal. Vector power meter C detects the second phase-shifted signal and the second reflected signal to obtain the phase difference between the reflected signal and the phase-shifted signal.

[0014] The amplitude ratio of the reflected signal to the incident signal is:

[0015]

[0016] Among them, V i The amplitude of the incident signal, V r This represents the amplitude of the reflected signal.

[0017] The phase difference between the reflected signal and the incident signal is:

[0018] in The phase of the incident signal, The phase of the reflected signal.

[0019] A third aspect of the present invention is the application of an automatic impedance matching system based on reflection coefficient measurement in a plasma excitation device. The parameters of the plasma excitation device are: power 0-10kW, operating frequency 1MHz-2.7GHz, and coupling method either inductive or capacitive coupling.

[0020] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0021] 1. This invention provides a fast, convenient, and accurate matching method for radio frequency loads, including plasma excitation devices. This method avoids blind operation and simplifies the matching process.

[0022] 2. This invention also provides a method for measuring the reflection coefficient of high-power active radio frequency devices, which can obtain the reflection coefficient containing complete amplitude and phase information, and realize accurate analysis of the impedance characteristics of high-power active radio frequency devices.

[0023] 3. The method proposed in this invention can be used in radio frequency circuits with a wide range of frequencies and power, various types of matching networks, and various forms of plasma excitation devices. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the technical scheme for an automatic matching method for plasma excitation devices based on reflection coefficient measurement.

[0025] Figure 2 A flowchart illustrating the implementation of an automatic matching method for plasma excitation devices based on reflection coefficient measurements.

[0026] Figure 3 This is a schematic diagram of the amplitude and phase measurement technology scheme for the reflectometer module.

[0027] Figure 4 This is an image showing the reflection coefficient measurement results from the reflectometer module.

[0028] Figure 5 This is a schematic diagram of the automatic control module.

[0029] Figure 6 Image of the automatic control module.

[0030] Figure 7 To generate plasma images.

[0031] Figure 8 A schematic diagram of the matching network used in conjunction with this system. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments. The following embodiments are merely descriptive and not limiting, and should not be construed as limiting the scope of protection of the present invention.

[0033] This invention provides an automatic matching system and method for plasma excitation devices based on reflection coefficient measurement. Figure 1 This is a schematic diagram of the technical solution adopted in this invention. The radio frequency (RF) circuit from the RF power supply to the plasma excitation device provides power to the plasma excitation device. The matching system proposed in this invention includes three parts: a reflectometer module, a matching network, and a control module. The reflection coefficient measured by the reflectometer module at the output of the RF power supply provides a reference for adjusting the matching network. The control module adjusts the matching network according to the measured reflection coefficient. After proper adjustment, the matching network ultimately matches the plasma excitation device with the RF power supply and achieves maximum power.

[0034] Figure 2 The specific implementation flow of the method provided by this invention is as follows: Step 1, using a reflectometer module connected in series between the matching network and the RF power supply, the reflection coefficient in the circuit is measured in real time and its position on the Smith chart is displayed. The measured reflection coefficient includes both amplitude and phase information, which can accurately and in real time indicate the impedance matching status of the plasma excitation device, providing guidance for the adjustment of the matching network; Step 2, the matching network is adjusted by changing the parameters of the variable elements in the matching network. The impedance matching status of the plasma excitation device changes, and the reflection coefficient and its position on the Smith chart move accordingly. The movement trajectory is close to a part of a circle or ellipse. When different variable elements are adjusted, the movement... The movement trajectories are also different. By changing different variable elements and observing the movement trajectory of the reflection coefficient on the Smith chart, the correspondence between the two can be obtained. Step 3: Based on the correspondence, further adjust the matching network so that the reflection coefficient approaches the origin of the Smith chart after passing through multiple different approximate circles or ellipses, and continuously decreases. Step 4: During the adjustment process, if the reflection coefficient is small enough that the RF power supply shows no reflected power, it is considered that the reflection has been eliminated and matching has been achieved. If the RF power supply still shows reflected power, it means that the reflection coefficient is still large, and steps 2 and 3 need to be tried again on the current basis until the reflection is eliminated and impedance matching is achieved.

[0035] Figure 3This is a schematic diagram of the technical solution for the reflectometer module. The reflectometer module is used to measure the reflection coefficient in the circuit, separate the reflected signal and the incident signal from the circuit, adjust the two signals, perform amplitude and phase detection, and further process the detection results to obtain an accurate reflection coefficient containing complete information. The reflectometer module consists of directional couplers, attenuators, phase shifters, vector power meters, analog-to-digital converters, and a first microcontroller module. Three directional couplers are connected to the power transmission line from the signal source to the plasma excitation device, coupling out two incident signals and one reflected signal from the line, respectively. Among them, the reflected signal and one incident signal are compressed in amplitude by the attenuator, and the other incident signal is phase-shifted and attenuated by the phase shifter, becoming a phase-shifted signal. The phase-shifted signal, the attenuated incident signal, and the reflected signal are each divided into two equal parts by the power divider, becoming a first incident signal, a second incident signal, a first reflected signal, a second reflected signal, a first phase-shifted signal, and a second phase-shifted signal. The vector power meters can distinguish the amplitude ratio and the absolute value of the phase difference between the two signals, therefore vector power meters A, B, and C are set. Vector power meter A detects the phase difference between the first phase-shifted signal and the first incident signal to obtain the phase shift magnitude provided by the phase shifter. Vector power meter B detects the second incident signal and the first reflected signal to obtain the amplitude ratio and phase difference between the reflected signal and the incident signal. The amplitude ratio of the reflected signal to the incident signal is the amplitude ratio part of the reflection coefficient, but this phase difference information is incomplete, ranging only from 0 to 180°. Vector power meter C detects the second phase-shifted signal and the second reflected signal to obtain the phase difference between the reflected signal and the phase-shifted signal. The first microcontroller module controls the analog-to-digital converter to read the measurement results from the three vector power meters, processes them to obtain the reflection coefficient, and displays the results on a screen or sends them via serial port to the automatic control module that adjusts the matching network.

[0036] There is a relationship between the incident signal and the phase-shifted signal:

[0037]

[0038] The complex amplitude of the incident signal is The complex amplitude of the reflected signal is The complex amplitude of the phase-shifted signal is V i V r V' i These are the amplitudes of the incident signal, the reflected signal, and the phase-shifted signal, respectively. These are the phases of the incident signal, the reflected signal, and the phase-shifted signal, respectively. It is the phase added to the phase-shifted signal by the phase shifter. Because the phase shift characteristics of the phase shifter are known, The sign and approximate range are determined, and the accurate value is measured by vector power meter A.

[0039] Vector power meter B detects the incident and reflected signals, and obtains the amplitude ratio of the two signals as follows:

[0040]

[0041] This gives us the amplitude information of the reflection coefficient.

[0042] Vector power meter B measured the phase difference between the reflected and incident signals as follows: The phase difference measured by vector power meter B actually corresponds to two results, denoted as follows: The result is correct, but the measurement result of vector power meter B alone cannot rule out another result.

[0043] Vector power meter C measures the phase difference between the reflected signal and the phase-shifted signal. This also corresponds to two outcomes. Will Each plus get in The measurement results of vector power meter B Similarly, both contain correct reflection coefficient phase information.

[0044] By processing, comparing, and analyzing the measurement results of vector power meters B and C in this way, an accurate and complete reflection coefficient can be obtained.

[0045] Preferably, the directional coupler is SYDC-20-31HP+, the attenuator is implemented by a resistor network, the phase shifter is implemented by a resistor and capacitor network, the vector power meter is AD8302, the analog-to-digital converter is ADS1118, and the first microcontroller is STM32F103RCT6.

[0046] Figure 4 This is the reflection coefficient measurement result from the reflectometer module. The upper area of ​​the reflectometer module screen displays a simplified Smith chart, with the reflection coefficient's position marked by a red dot. Below the Smith chart, the analog-to-digital converter's conversion result and the amplitude ratio and phase difference included in the reflection coefficient are displayed.

[0047] Figure 5 This is the schematic diagram of the automatic control module. The second microcontroller receives the measurement results from the reflectometer module via a serial port and controls the motor via a driver to rotate the variable capacitor in the matching network, thus changing the capacitance value. The user can start / stop the matching or manually control the motor rotation using buttons on the control panel. The display shows the Smith chart, the measured reflectance coefficient, and the current operating status of the control module.

[0048] Figure 6This is a physical diagram of the automatic control module. The plasma excitation distance is 2mm. Preferably, the second microcontroller is an STM32F103RCT6, and the motor is a 42-stepper motor.

[0049] Figure 7 The left side shows an image of the plasma excited by the plasma excitation device after impedance matching. The parameters of the radio frequency power supply are as follows: Figure 7 As shown on the right, the reflected power is zero, indicating a good match.

[0050] The matching network diagram used in conjunction with this is as follows: Figure 8 As shown, it consists of variable capacitors C1 and C2 and inductor L; AC is the RF power supply, R... S Z is the internal resistance of the RF power supply. L The load is the impedance of the plasma excitation device. The relevant excitation parameters are shown in Table 1. Using the described method, matching was achieved within 5 minutes under manual control and within 1 minute under automatic control. In contrast, directly using a commercially available RF power supply manual matching device (Institute of Microelectronics, Chinese Academy of Sciences, RFM500 manual RF matching device) without the described method would take approximately one week.

[0051] Table 1 Plasma excitation parameters

[0052] RF power 30W Excitation gas helium Excitation device head type Capacitive coupling Capacitor C1 in the matching network 45pF Capacitor C2 in the matching network 540pF Inductor L in the matching network 1μH

[0053] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all fall within the protection scope of the present invention.

Claims

1. An automatic impedance matching system based on reflection coefficient measurement, comprising a matching network, characterized in that, Also includes: Reflectometer module and control module, The reflectometer module is connected in series between the matching network and the RF power supply. The reflectometer module is used to measure the reflection coefficient at the output of the RF power supply. The reflection coefficient includes both amplitude and phase information. The control module adjusts the matching network to change the position of the reflection coefficient on the Smith chart, making it infinitely close to the origin of the Smith chart. The RF power supply displays a reflected power of 0, thus achieving impedance matching. The reflectometer module includes: A directional coupler couples out two incident signals and one reflected signal from the line. An attenuator is used to compress the amplitude of the first incident signal and the reflected signal; The phase shifter converts the second incident signal into a phase-shifted signal. The power divider splits the phase-shifted signal, the attenuated incident signal, and the reflected signal into two parts. The vector power meter is connected to the signal output terminal of the power divider and is used to identify the amplitude ratio and phase difference of the two signals after the signal is split into two. The first microcontroller controls the analog-to-digital converter to read the measurement results of the vector power meter, processes them to obtain the reflection coefficient, displays the results on the display screen, or sends them to the automatic control module that adjusts the matching network.

2. The automatic impedance matching system based on reflection coefficient measurement according to claim 1, characterized in that, The control module includes: Electric motor; A driver, which is connected to a motor; The second microcontroller is connected to the driver. The second microcontroller receives the measurement results from the reflectometer module and controls the motor through the driver to drive the variable element parameter adjustment knob in the matching network to rotate, thereby adjusting the parameters of the variable element. A control panel is connected to the second microcontroller, and the user can start / stop the matching process via buttons on the control panel. The display screen shows the Smith chart, the measured reflectance coefficient, and the current operating status of the control module.

3. A matching method for an automatic impedance matching system based on reflection coefficient measurement according to claim 1 or 2, characterized in that, The reflectometer module measures the reflection coefficient in real time and marks it on the Smith chart. The control module adjusts the matching network, changing the parameters of the variable elements in the matching network. The reflection coefficient and its position on the Smith chart move accordingly, with the movement trajectory approximating a part of a circle or ellipse. By changing different variable elements and observing the movement trajectory of the reflection coefficient on the Smith chart, the correspondence between the two can be obtained. Based on the correspondence, the matching network is further adjusted so that the reflection coefficient approaches the origin of the Smith chart after passing through multiple different approximate circular or elliptical trajectories, thus eliminating reflection.

4. The matching method according to claim 3, characterized in that, The phase-shifted signal, attenuated incident signal, and reflected signal are each divided into two equal parts by a power divider, resulting in a first incident signal, a second incident signal, a first reflected signal, a second reflected signal, a first phase-shifted signal, and a second phase-shifted signal. Three vector power meters are used: Vector Power Meter A, Vector Power Meter B, and Vector Power Meter C. Vector Power Meter A detects the phase difference between the first phase-shifted signal and the first incident signal to obtain the phase shift magnitude provided by the phase shifter. Vector Power Meter B detects the second incident signal and the first reflected signal to obtain the amplitude ratio and phase difference between the reflected and incident signals. Vector Power Meter C detects the second phase-shifted signal and the second reflected signal to obtain the phase difference between the reflected and phase-shifted signals.

5. The matching method according to claim 4, characterized in that, The amplitude ratio of the reflected signal to the incident signal is: Among them, V i The amplitude of the incident signal, V r This represents the amplitude of the reflected signal.

6. The matching method according to claim 4, characterized in that, The phase difference between the reflected signal and the incident signal is: in The phase of the incident signal, The phase of the reflected signal.

7. The application of the automatic impedance matching system based on reflection coefficient measurement as described in claim 1 or 2 in a plasma excitation device.

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